What: The social network for sharing images that spawned countless copy cats and was most recently valued at $5 billion.Fashion is more visible, shareable and viral than ever, thanks in large part to its presence as a core part of what populates Pinterest, the San Francisco company best known for making scrolling walls of images a constant and a norm of today’s online experience. The hotly anticipated rollout of paid advertising this spring through Promoted Pins stands to make the network even more attractive to brands.

Why it’s addictive: The network’s increasing popularity among consumers, as well as the confluence of brands and retailers using it as a marketing tool, have made it a choice place to discover the latest styles, new product launches and plenty of behind-the-scenes glimpses of designers, labels and fashion icons. www.pinterest.com

Pinterest, the San Francisco company that bills itself as a visual discovery tool, has become the social network of choice for collecting recipes, gardening ideas and images of the perfect wedding. The platform acts as a digital bulletin board where people can "pin" images of the things they'd like to wear, do or make and then share those pins with others via "boards."

But as retailers are discovering, it's also the mobile-era equivalent of flipping through a catalog - aspiring to a better, more perfect self. Pinterest's effect goes both ways: It influences what people buy, but also what retailers stock on their shelves.

The site's reach is wide - and growing rapidly. Pinterest is now more popular than Twitter, with more than a fifth of American adults using the site, according to the Pew Research Center. There are now more than 30 billion Pins on Pinterest, and more than 2 million fashion Pins are saved each day, according to the company.

Beauty and women's fashion are the fifth and sixth most popular categories on Pinterest, respectively, according to industry analyst RJ Metrics.

"We often hear people say they use their boards to develop a sense of style, organize looks and collect accessories, from fashion insiders to everyday Pinners," said Pinterest spokeswoman Mithya Srinivasan.

This combination of aesthetically driven, social-fueled desire is proving powerful. Users who click through Pins to e-commerce sites are 10 percent more likely to make a purchase than those referred by other social networks, and they usually spend more, according to Shopify. Pinterest has managed to turn aspiration into a product and mass opinion into a vehicle fordriving actual retail traffic.

And retailers have paid attention. Nordstrom, for one, is using real-time data from Pinterest to figure out what to display in stores. Items that hit big with the store's more than 4 million Pinterest followers online get more prominent display in store - a bid to rack up sales by showing shoppers what they seem to want.

As Ilse Metchek, president of the California Fashion Association, pointed out, Pinterest has given merchandisers an effective tool to determine what might be coming next. It's created a place of mass, real-time critique. In stores such as Nordstrom and Target, items that prove popular on Pinterest are marked with a tag displaying the Pinterest "P." Pinterest has become a way of giving a product status. Its newest tool, Guided Search, allows users to easily search for, say, a suit, and to narrow down choices with extreme specificity.

Brands fit in naturally with the Pinterest experience without feeling like advertising. That's why, as Pinterest has rolled out Promoted Pins - sponsored Pins that will appear in users' feeds - companies such as Banana Republic, Gap and Target have signed on.

Style Pins may trail categories such as food and DIY at this point, but the impact is still huge. And while Pinterest users are at present overwhelmingly female, men's fashion is a category quickly gaining tread.

Pinterest's real secret is that it has managed to make shopping feel like something more exalted.